1. Field of the Invention
The present invention relates to an electrifying apparatus for electrifying (charging) at least one of the surface of a latent-image supporting object, such as a photoconductor, and toner adhered to the surface by a conductive member to which bias is supplied while the conductive member is contacting the surface of the latent-image supporting object. The present invention further relates to a processing unit and an image formation apparatus using the electrifying apparatus.
2. Description of the Related Art
Generally, image formation apparatuses that employ an electronic photography method form an image according to the following processes. Namely, a electrostatic latent image is formed by exposure scanning a latent-image supporting object, such as a photoconductor, that is uniformly electrified; then the electrostatic latent image is developed into a toner image by a development apparatus. Subsequently, the toner image is either directly transferred onto a recording object such as paper from the latent-image supporting object, or transferred to the recording object through a middle transfer object.
According to a conventional electrifying apparatus used by the image formation apparatuses, an electric bias is provided to an electrifying roller serving as a conductive member that touches the surface of the latent-image supporting object so that the surface of the latent-image supporting object may be uniformly electrified by the conductive member.
Further, Patent Reference 1 discloses an electrifying apparatus that includes an auxiliary electrifying apparatus, to which auxiliary electrifying apparatus an auxiliary electric bias is provided. The auxiliary electrifying apparatus is provided in addition to a main electrifying apparatus for principally electrifying the latent-image supporting object such as an electrifying roller and an electrifying charger of a scorotron method. The auxiliary electrifying apparatus contacts a part of the peripheral surface of the latent-image supporting object, which is endlessly moving, after the latent image supporting object passes a transfer process location and before advancing into a location of a main electrifying process to be performed by the main electrifying apparatus. In this way, auxiliary electrifying of the surface of the latent-image supporting object is carried out and residual toner adhered to the surface is charged to have a regular polarity by discharging or charge injection by the auxiliary electrifying apparatus before the uniform electrifying is performed by the main electrifying apparatus. Thereby, charge unevenness of the latent-image supporting object can be reduced, and background dirt due to residual toner with a low charge or a reverse charge being conveyed to a development area can be prevented.
With the conventional electrifying apparatuses, if residual toner is fixed to the electrifying apparatus and the auxiliary electrifying apparatus (the conductive member) that contact the latent-image supporting object, discharging and charge injection between the conductive member, the residual toner, and the latent-image supporting object are interfered with. Accordingly, the main electrifying and the auxiliary electrifying are degraded; therefore, charge unevenness is generated, and electrifying of the residual toner is degraded, causing the background dirt to be generated. Here, the background dirt is a phenomenon of the toner adhering to the background part (uniformly charged part) of the latent-image supporting object.
Then, an electrifying apparatus disclosed by Patent Reference 2 specifies that the electrifying apparatus have a pure-water contact angle of greater than 90 degrees so that the toner adhesion to the electrifying apparatus is reduced.
[Patent Reference 1] JPA 2005-62737
[Patent Reference 2] JPA 11-352752
However, the inventors of the present invention found out by experiments that the toner adhesion to the conductive member, such as the electrifying apparatus, could not be reduced over a long period of time by only satisfying the condition that the pure-water contact angle be comparatively great. For example, a conductive member having a pure-water contact angle of 100 degrees caused toner adhesion after printing out thousands of sheets.